design and functionality

Short-focus,
wide-angle lenses are usually mounted near the film. Single-lens reflex cameras need a certain minimum lens-to-film distance to accommodate the swinging mirror. Wide-angle (and sometimes normal-focus) lenses for such cameras therefore use retrofocus designs. In these the back focus is appreciably longer than the focal length. Both a telephoto and a retrofocus lens must be specially...

research by Schlesinger

In addition to his parallax work at Allegheny, Schlesinger also pioneered in the use of wide-angle cameras for determining photographically stellar positions and proper motions (the apparent rates of change of position across an observer’s line of sight), formerly measured by laborious visual methods. Fifteen volumes of the
Yale Zone Catalogues, which were prepared under his direction,...

use of germanium

...detecting and measuring such radiation, such as windows and lenses. The high index of refraction of germanium dioxide renders it valuable as a component of glasses used in optical devices, such as
wide-angle lenses for cameras and microscope objectives. The toxicology of germanium and its compounds is poorly defined.